Method of producing ceramic body

ABSTRACT

A method of producing a ceramic body having a construction such that cells are plugged alternately at both end faces of a ceramic honeycomb structural body by filling a plugging slurry into predetermined cells at both end faces of a ceramic honeycomb formed body, having the steps of: filling a plugging material for mask into the cells to be opened at one end face of the ceramic honeycomb formed body; immersing the end face, to which the plugging material for mask is filled, into a plugging slurry; and drying and sintering the ceramic honeycomb formed body while the plugging material for mask is removed during a drying step or a sintering step.

TECHNICAL FIELD

[0001] The present invention relates to a method of producing a ceramicbody having a construction such that cells are plugged alternately atboth end faces of a ceramic honeycomb structural body.

BACKGROUND ART

[0002] Up to now, in order to produce a ceramic body in which cells areplugged alternately at both end faces of a ceramic honeycomb structuralbody, various producing methods have been known. FIGS. 15a-15 c areschematic views respectively explaining one embodiment of a method ofproducing such a known ceramic body. According to FIGS. 15a-15 c, oneembodiment of the known method of producing the ceramic body will beexplained. At first, as shown in FIG. 15a, a mask 54 made of rubberhaving holes 53 corresponding to cells 52 to be plugged at an end faceof a ceramic honeycomb formed body 51 (ceramic honeycomb structural bodybefore sintering) is prepared, and the thus prepared mask 54 is set at apredetermined position on the end face of the ceramic honeycomb formedbody 51 by hand.

[0003] Then, as shown in FIG. 15b, the end face of the ceramic honeycombformed body 51, to which thee mask 54 is set, is immersed in a pluggingslurry 55, and, a pressure is applied to the ceramic honeycomb formedbody 51 from above, so that the cells 52 are filled with the slurry 55through the holes 53 of the mask 54. At the other end face of theceramic honeycomb formed body 51, predetermined cells 52 are filled withthe slurry 55 in the same manner. in this case, a mask having a reversehole pattern such that holes are arranged at portions where no holes 53of the mask 54 are arranged is used so as to obtain a construction suchthat the cells 52 are plugged alternately at both end faces of theceramic honeycomb structural body. According to the processes mentionedabove, as shown in FIG. 15c by cross section, it is possible to obtainthe ceramic honeycomb formed body 51 having a construction such thatthee cells 2 are plugged alternately at its both end faces. Finally, thethus obtained ceramic honeycomb body 51 is sintered so as to obtain aceramic body according to the invention.

[0004] However, in the method of producing the known ceramic bodymentioned above, it is difficult to make the mask 54 having thepredetermined holes 53 and to set the mask 54 accurately on the end faceof the ceramic honeycomb formed body 51. Particularly, in a large sizeceramic body having a diameter of about 300 mm which is recentlyrequired, the number of cells 52 at the end face reaches to fewten-thousands, and thus the difficulties mentioned above become worse.Moreover, since the mask 54 is set on the end face of the ceramichoneycomb formed body 51 by hand, it is necessary for a worker to getskillful and this setting operation requires much time. In addition,there is a problem such that this setting operation is not automated.Further, after the plugging operation, it is necessary to perform acleaning operation of the mask 54 for recycling. However, since the mask54 has a large number of cells as mentioned above, there is a problemsuch that it is very difficult to clean up the mask 54.

DISCLOSURE OF INVENTION

[0005] An object of the invention is to eliminate the drawbacksmentioned above and to provide a method of producing a ceramic bodywhich can easily plug cells at an end face and which can be easilyautomated.

[0006] According to a method of producing a ceramic body according tothe invention, a method of producing a ceramic body having aconstruction such that cells are plugged alternately at both end facesof a ceramic honeycomb structural body by filling a plugging slurry intopredetermined cells at both end faces of a ceramic honeycomb formedbody, comprises the steps of: filling a plugging material for mask intothe cells to be opened at one end face of the ceramic honeycomb formedbody; immersing the end face, to which the plugging material for mask isfilled, into a plugging slurry; and drying and sintering the ceramichoneycomb formed body while the plugging material for mask is removedduring a drying step or a sintering step.

[0007] In the present invention, since a plugging operation of the endface of the ceramic honeycomb structural body is performed by using aplugging material for mask which can be removed at the sintering withoutusing a mask, it is possible to eliminate a production of the mask and asetting operation of the mask with respect to the end face of theceramic honeycomb structural body. Moreover, since a filling operationof various plugging materials for mask mentioned below can be easilyautomated, the plugging operation of the ceramic body according to theinvention can be also automated.

[0008] As a preferred embodiment of the invention, the plugging materialfor mask filling step further comprises the steps of: preparing asuction jig having a same honeycomb construction as that of the ceramichoneycomb formed body; adhering a mask, in which holes are arrangedcorresponding to the cells to be plugged, to one end face of the suctionjig; sucking paraffin balls, a diameter of which is larger than a lengthof one side of the cell, to the predetermined cells at the other endface by sucking from the end face to which the mask is adhered; settingthe suction jig, to which paraffin balls are sucked, to the end face ofthe ceramic honeycomb formed body to which the plugging material is tobe filled; aligning the paraffin balls to the cells to be opened bystopping the sucking operation; inserting the thus aligned paraffinballs into the cells by applying pressure; and filling the paraffinballs into the cells to be opened as the plugging material for mask.Moreover, the plugging material for mask filling step further comprisesthe steps of: making a mask for respective ceramic honeycomb formedbodies by piercing a sheet adhered to one end face of the ceramichoneycomb formed body at positions corresponding to the cells to beplugged; immersing the one end face to which the mask is adhered into aliquid paraffin; inserting the liquid paraffin into the cells throughthe holes of the mask by applying a pressure; and filling the liquidparaffin into the cells to be opened as the plugging material for mask.Further, the plugging material for mask filling step further comprisesthe steps of: immersing one end face of the ceramic honeycomb formedbody into a photo-curing resin before hardening; emanating a light tothe photo-curing resin from the other end face through a mask, in whicha light is transmitted only to the cells to be opened, so as to hardenthe photo-curing resin; and filling the photo-curing resin into thecells to be opened as the plugging material for mask. In all thepreferred embodiments mentioned above, it is possible to perform afilling operation of the plugging material for mask with respect to theceramic honeycomb structural body effectively, and thus it is preferred.

BRIEF DESCRIPTION OF THE INVENTION

[0009]FIGS. 1a-1 c are schematic view respectively explaining one stepof a paraffin ball filling method as one example of a method ofproducing a ceramic body according to the invention.

[0010]FIGS. 2a-2 d are schematic views respectively explaining anotherstep in the method shown in FIG. 1.

[0011]FIGS. 3a and 3 b are schematic views respectively explaining stillanother step in the method shown in FIG. 1.

[0012]FIGS. 4a-4 c are schematic views respectively explaining stillanother step in the method shown in FIG. 1.

[0013]FIG. 5 is a schematic view showing one embodiment of a ceramicbody according to the invention.

[0014]FIGS. 6a and 6 b are schematic views respectively showing oneembodiment of a paraffin ball aligning method in the embodiment shown inFIG. 1.

[0015]FIGS. 7a-7 d are schematic views respectively showing anotherexample of a paraffin ball aligning method in the embodiment method inthe embodiment shown in FIG. 1.

[0016]FIG. 8 is a schematic view explaining one step of a liquidparaffin filling method as another example of a method of producing aceramic body according to the invention.

[0017]FIGS. 9a and 9 b are schematic views respectively explaininganother step in the embodiment shown in FIG. 8.

[0018]FIGS. 10a and 10 b are schematic views respectively explainingstill another step in the embodiment shown in FIG. 8.

[0019]FIGS. 11a-11 c are schematic views respectively explaining stillanother step in the embodiment shown in FIG. 8.

[0020]FIG. 12 is a schematic view explaining one step of a photo-curingresin filling method as still another example of a method of producing aceramic body according to the invention.

[0021]FIGS. 13a-13 c are schematic views respectively explaining anotherstep in the embodiment shown in FIG. 12.

[0022]FIGS. 14a and 14 b are schematic view respectively explainingstill another in the embodiment shown in FIG. 12.

[0023]FIGS. 15a-15 c are schematic views respectively explaining oneembodiment of the known method of producing a ceramic body.

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] The most important features of the invention is to perform thesteps of: filling a plugging material for mask such as paraffin andphoto-curing resin into cells to be opened of a ceramic honeycomb formedbody; filling a plugging slurry into the cells to which the pluggingmaterial for mask is not filled; sintering the ceramic honeycomb formedbody; and removing the plugging material for mask at the sintering step.As the ceramic honeycomb formed body, use is made of the known ceramichoneycomb formed body made of cordierite and so on. The ceramichoneycomb formed body can be produced according to the known manner byextruding raw material mixture from a die. Hereinafter, according to adifference of filling methods of the plugging material for mask, theembodiments (1) method of filling paraffin balls, (2) method of fillingliquid paraffin through holes arranged to a sheet, and (3) method offilling photo-curing resin will be explained.

[0025] (1) As to a method of filling paraffin balls:

[0026] {circle over (1)} Firstly, as shown in FIGS. 1a-1 c, paraffinballs 3 having a diameter larger than a length of one side of cell 2constituting a ceramic honeycomb formed body 1 are prepared, and thethus prepared paraffin balls 3 are aligned in a checkered pattern on thecells 2 to be opened at an end face of the ceramic honeycomb formed body1. A method of aligning the paraffin balls 3 will be explainedhereinafter in detail. In FIG. 1c, the paraffin balls 3 are shown largeras compared with their actual size so as to see them.

[0027] After aligning the paraffin balls 3 on the end face, as shown inFIGS. 2a and 2 b, the paraffin balls 3 are inserted into the cells byapplying a pressure thereto. In this case, the paraffin ball 3 is groundor deformed by a wall of the cell 2, and a space occurs between theparaffin ball 3 and an inner wall of the cell 2. Therefore, as shown inFIGS. 2c and 2 d, the paraffin ball 3 is softened by heat and adapted tothe inner wall of the cell 2 without spaces.

[0028] {circle over (2)} Then, as shown in FIG. 3a, the ceramichoneycomb formed body 1 is set to a vacuum apparatus 4 which canfunction to vacuum only a center portion other than an outer peripheralportion of the ceramic honeycomb formed body 1 under a condition suchthat the end face of the ceramic honeycomb formed body 1 after theparaffin balls 3 are inserted into the predetermined cells 2 ispositioned upward. Under such a condition, the ceramic honeycomb formedbody 1 approaches to a tray 5 in which the paraffin balls 3 are filled,and the vacuum apparatus 4 starts to work. In this case, a vacuum stateoccurs only at the cells 2 to which the paraffin balls 3 are not filledat an upper end face of the ceramic honeycomb formed body 1, and thusthe paraffin balls 3 are sucked to the predetermined cells 2 at an underend face. After that, as mentioned above, the paraffin balls 3 areinserted into the cells 2. In this manner, as shown in FIG. 3b, theparaffin balls 3 are filled into the cells 2 to be opened at the bothend faces of the ceramic honeycomb formed body 1 as a plugging materialfor mask.

[0029] {circle over (3)} Then, as shown in FIG. 4a, the end face of thethus obtained ceramic honeycomb formed body 1 is immersed into aplugging slurry 7 stored in a vessel 6. Then, as shown in FIG. 4b, theplugging slurry 7 is filled into the predetermined cells 2, to which theparaffin balls 3 are not filled, by applying a pressure to the ceramichoneycomb formed body 1 from upward by means of a pressurized means 8.The same operations are performed repeatedly with respect to the otherend face. As a result, as shown in FIG. 4c, it is possible to obtain theceramic honeycomb formed body 1 in which the plugging slurry 7 is filledinto the cells 2 at the both end faces to which the paraffin balls 2 arenot filled.

[0030] {circle over (4)} Then, the thus obtained ceramic honeycombformed body 1 is sintered as is the same manner as that of the knownmanner after drying. At the drying step or the sintering step, theplugging slurry 7 is dried and sintered so as to integrate with a cellwall 9. At the same time, the paraffin balls 3 are melted and removed.As a result, as shown in FIG. 5, it is possible to obtain a ceramic body10 having a construction such that the cells 2 are plugged alternatelyat the both end faces of the ceramic honeycomb structural body.

[0031] {circle over (5)} As mentioned above, the method of filling theparaffin balls are finished. Hereinafter, as a preferable method ofaligning the paraffin balls 3 to the predetermined cells 2, (a) methodof utilizing a setter (formed body having the same honeycomb structureas that of the ceramic honeycomb formed body) as a paraffin ball suctionjig, and (b) method of utilizing the ceramic honeycomb formed bodyitself as the paraffin ball suction jig will be explained.

[0032] (a) As to a method of utilizing the setter as the paraffin ballsuction jig (FIGS. 6a and 6 b):

[0033] In this method, a setter 21 is formed simultaneously when theceramic honeycomb formed body 1 is formed and is utilized as the suctionjig. A mask 23 having a construction such that holes 22 are arranged ina checkered pattern at positions corresponding to the cells to beplugged is adhered to an upper face of the setter 21. The mask 23 may beformed by rubber, resin, paper and so on. The setter 21 is set to thevacuum apparatus 4 in such a manner that the surface, to which the mask23 is adhered, is positioned upward. Then, the setter 21 approaches tothee tray 5 in which the paraffin balls 3 are stored, and the suctionapparatus 4 starts to work. As a result, the paraffin balls 3 are suckedin a checkered pattern on an under face of the setter 21. Then, thesetter 21 is set on the end face of the ceramic honeycomb formed body Ipositioned by for example an image processing apparatus, and the vacuumapparatus 4 is stopped. In this manner, the paraffin balls 3 are alignedto the end face of the ceramic honeycomb formed body 1. Then, the samealigning operations are performed for the other end face by utilizingthe setter 21, to which another mask 23 is adhered, so that theeparaffin balls 3 can be aligned at the both end faces.

[0034] (b) As to a method of utilizing the ceramic honeycomb formed bodyitself as the paraffin ball suction jig (FIGS. 7a-7 d):

[0035] In this method, the ceramic honeycomb formed body 1, in which theparaffin balls 2 are filled to the cells 2 at one end face, is utilizedas the suction jig for filling the paraffin balls 3 to a next ceramichoneycomb formed body 1. At first, as shown in FIG. 7a, a ceramichoneycomb formed body 1-1, to which the mask 23 is adhered, is utilizedfor the first ceramic honeycomb formed body 1. Then, the paraffin balls3 are aligned to the predetermined cells 2 at the end face of a nextceramic honeycomb formed body 1-2 in the same manner as that of theembodiment mentioned above except that the ceramic honeycomb formed body1-1 is utilized as the setter 21 (FIG. 7b). After that, the paraffinballs 3 are aligned to the predetermined cells 2 at the end face of afurther next ceramic honeycomb formed body 1-3 (FIG. 7d) in the samemanner as that of the embodiment mentioned above except that the ceramichoneycomb formed body 1-2, in which the paraffin balls 3 are aligned atone end face, is utilized as the setter 21 (FIG. 7c). The aboveoperations are repeated, so that the paraffin balls 3 are aligned at theboth end faces.

[0036] (2) As to a method of filling liquid paraffin through holesarranged to a sheet:

[0037] {circle over (1)} Firstly, as shown in FIG. 8, an image of theend face of the ceramic honeycomb formed body 1 is picked-up by a camera31, and the thus picked-up image is subjected to an image processing. Inthis manner, positions of all the cells 2 at the end face arerecognized.

[0038] {circle over (2)} Then, as shown in FIG. 9a, a sheet 32 having adimension substantially equal to the end face of the ceramic honeycombformed body 1 is prepared. Then, as shown in FIG. 9b, the thus preparedsheet 32 is adhered to the overall end face, the cell positions of whichare recognized. As the sheet 32, a commercially available adhesive sheetcan be used.

[0039] {circle over (3)} Then, as shown in FIGS. 10a and 10 b, referencepositions of small blocks defined according to a specification of theceramic honeycomb formed body 1 such as outer diameter and cell pitchare calculated on the basis of the cell positions which are recognizedby an image processing, and holes 33 are opened at the cell positions tobe opened of the sheet 32 by means of a laser machining and so on, whilethe ceramic honeycomb formed body 1 is positioned by means of an XYZθstage. The sheet 32 having the holes 33 functions as the mask. The hole33 has a circular shape, and it is not necessary to open to an extentsuch that the hole 33 has the same (quadrangle) shape as that of thecell 2. Therefore, even in the case that a slight cell pitch variationoccurs at the end face, there is no risk for piercing a cell wall andfurther a next cell, since a diameter of the hole 33 is smaller than thecell 2. In this case, it is preferred to set a diameter of the hole 33corresponding to a viscosity of a melted liquid-like paraffin in such amanner that it is smaller when the viscosity is low and it is largerthen the viscosity is high. Moreover, it is preferred to perform theabove hole machining with respect to the sheet 32 for respective smallblocks that are formed by dividing the cells 2 at the end face, but itis possible to perform the hole machining with respect to the overallend face. When the hole machining is performed for respective smallblocks one by one, it is possible to perform the hole machiningcorrectly, since variations of cell shape and cell pitch are small insuch a small block region.

[0040] {circle over (4)} Then, as shown in FIGS. 11a-11 c, a meltedliquid paraffin 34 is filled into the cells 2 through the holes 33 ofthe sheet 32. That is to say, as shown in FIG. 11a, the end face towhich the sheet 32 having the holes 33 is adhered is immersed into theliquid paraffin 34 in a vessel 35. Then, as shown in FIG. 11b, theceramic honeycomb formed body 1 is pressed by utilizing a pressurizedmeans 36, so that the liquid paraffin 34 is inserted by pressure intothe cells 2 through the holes 33 of the sheet 32. Then, as shown in FIG.11c, the sheet 32 is removed from the end face, and a paraffin fillingoperation for one end face is finished. After that, the same paraffinfilling operation as mentioned above is performed for the other endface, and it is possible to obtain the ceramic honeycomb formed body 1in which the predetermined cells 2 are filled with the liquid paraffin34 at the both end faces.

[0041] {circle over (5)} Then, as explained by the previous embodimentshown in FIGS. 4a-4 c, the plugging slurry 7 is filled into the cells 2that are not plugged by the liquid paraffin 34 (corresponding to theparaffin 3 in FIG. 4) according to the known method. After that, thethus obtained ceramic honeycomb formed body 1 is dried and sintered, sothat the paraffin 34 is removed and the plugging slurry 7 is integratedwith the cell wall. Accordingly, it is possible to obtain the ceramicbody 10 as shown in FIG. 5.

[0042] (3) As to a method of filling a photo-curing resin:

[0043] {circle over (1)} Firstly, as shown in FIG. 12, one end face ofthe ceramic honeycomb formed body 1 is immersed into a liquidphoto-curing resin 41 before hardening stored in a tray 42. Then, animage of the other face of the ceramic honeycomb formed body 1 ispicked-up by a camera 43, and the picked-up image is subjected to animage processing so as to recognize positions of all the cells 2 at theend face. In this case, it is possible to use the known photo-curingresin as the photo-curing resin 41.

[0044] {circle over (2)} Then, as shown in FIG. 13a, a mask 44 utilizinga liquid crystal is set to the end face of the ceramic honeycomb formedbody 1 to which the cell positions are recognized, and the mask 44 isvaried in a checkered pattern in such a manner that a light isintroduced only to the cells to be opened on the basis of the positiondata of all the cells 2 obtained by an image processing. Then, as shownin FIG. 13b, a light emanating from a light source 45 is introduced tothe end face of the ceramic honeycomb formed body 1 through the mask 44.By introducing a light through the cells 2, the photo-curing resinexisting at thee cells 2, through which a light is transmitted, ishardened. Moreover, as shown in FIG. 13c, the end face of the ceramichoneycomb formed body 1 is plugged by the hardened resin.

[0045] {circle over (3)} As to the other end face, the plugged resin 41functions as the mask, since a light is shielded by the plugged resin.Therefore, as shown in FIG. 14a, the other end face is immersed into thephoto-curing resin 41 stored in the tray 42, and a light emanating fromthe light source 45 is introduced to the end face of the ceramichoneycomb formed body 1. In this manner, as shown in FIG. 14b, thephoto-curing resin 41 existing in the desired cells 2 is hardened. Inthis case, in order to plug all the outer peripheral portion of theceramic honeycomb formed body 1, a light is not introduced to thephoto-curing resin 41 at a peripheral portion by using a fixed mask 46as shown in FIG. 14a.

[0046] {circle over (4)} Then, as explained by the previous embodimentshown in FIGS. 4a-4 c, the plugging slurry 7 is filled into the cells 2that are not plugged by the photo-curing resin 41 (corresponding to theparaffin 3 in FIG. 4) according to the known method. After that, thethus obtained ceramic honeycomb formed body 1 is dried and sintered, sothat the photo-curing resin 41 is removed and the plugging slurry 7 isintegrated with the cell wall. Accordingly, it is possible to obtain theceramic body 10 as shown in FIG. 5.

[0047] Industrial Applicability

[0048] As clearly understood from the above explanations, according tothe invention, since a plugging operation of the end face of the ceramichoneycomb structural body is performed by using a plugging material formask which can be removed at the sintering without using a mask, it ispossible to eliminate a production of the mask and a setting operationof the mask with respect to the end face of the ceramic honeycombstructural body. Moreover, since a filling operation of various pluggingmaterials for mask can be easily automated, the plugging operation ofthe ceramic body according to the invention can be also automated.

1. A method of producing a ceramic body having a construction such thatcells are plugged alternately at both end faces of a ceramic honeycombstructural body by filling a plugging slurry into predetermined cells atboth end faces of a ceramic honeycomb formed body, comprising the stepsof: filling a plugging material for mask into the cells to be opened atone end face of the ceramic honeycomb formed body; immersing the endface, to which the plugging material for mask is filled, into a pluggingslurry; and drying and sintering the ceramic honeycomb formed body whilethe plugging material for mask is removed during a drying step or asintering step.
 2. The method of producing a ceramic body according toclaim 1, wherein the plugging material for mask filling step furthercomprising the steps of: preparing a suction jig having a same honeycombconstruction as that of the ceramic honeycomb formed body; adhering amask, in which holes are arranged corresponding to the cells to beplugged, to one end face of the suction jig; sucking paraffin balls, adiameter of which is larger than a length of one side of the cell, tothe predetermined cells at the other end face by sucking from the endface to which the mask is adhered; setting the suction jig, to whichparaffin balls are sucked, to the end face of the ceramic honeycombformed body to which the plugging material is to be filled; aligning theparaffin balls to the cells to be opened by stopping the suckingoperation; inserting the thus aligned paraffin balls into the cells byapplying pressure; and filling the paraffin balls into the cells to beopened as the plugging material for mask.
 3. The method of producing aceramic body according to claim 2, wherein the improvement furthercomprising the steps of: sucking the paraffin balls to the other endface by sucking from the one end face to which the paraffin balls arefilled; inserting the thus sucked paraffin balls into the cells byapplying a pressure; and filling the paraffin balls into the cells to beopened of the other end face.
 4. The method of producing a ceramic bodyaccording to claim 2, wherein the ceramic honeycomb formed body, inwhich the paraffin balls are filled into the cells of the one end face,is used as the suction jig for filling the paraffin balls of the nextceramic honeycomb formed body.
 5. The method of producing a ceramic bodyaccording to claim 1, wherein the plugging material for mask fillingstep further comprising the steps of: making a mask for respectiveceramic honeycomb formed bodies by piercing a sheet adhered to one endface of the ceramic honeycomb formed body at positions corresponding tothe cells to be plugged; immersing the one end face to which the mask isadhered into a liquid paraffin; inserting the liquid paraffin into thecells through the holes of the mask by applying a pressure; and fillingthe liquid paraffin into the cells to be opened as the plugging materialfor mask.
 6. The method of producing a ceramic body according to claim5, wherein the piercing step to the sheet adhered to one end face of theceramic honeycomb formed body further comprising a step of: dividing thecells of the end face into a plurality of small blocks; and performingthe piercing for respective small blocks one by one.
 7. The method ofproducing a ceramic body according to claim 1, wherein the pluggingmaterial for mask filling step further comprising the steps of:immersing one end face of the ceramic honeycomb formed body into aphoto-curing resin before hardening; emanating a light to thephoto-curing resin from the other end face through a mask, in which alight is transmitted only to the cells to be opened, so as to harden thephoto-curing resin; and filling the photo-curing resin into the cells tobe opened as the plugging material for mask.
 8. The method of producinga ceramic body according to claim 7, wherein the plugging material formask filling step further comprising the steps of: immersing the otherend face of the ceramic honeycomb formed body into a photo-curing resinbefore hardening; emanating a light to the photo-curing resin from theone end face through a mask, in which a light is transmitted only to thecells to be opened, so as to harden the photo-curing resin; and fillingthe photo-curing resin into the cells to be opened as the pluggingmaterial for mask.